Fibroblast Modulation of Stem Cell Lineage Infidelity and Metaplasia in Tissue Fibrosis

Epithelial stem cells are segregated on the basis of region-specific identities during homeostasis. However, tissue perturbations can induce remarkable plasticity in stem cells to adopt lineage identities outside their anatomical compartments. This phenomenon has been termed lineage infidelity or metaplasia depending on the tissue, and the stem cell trajectory can determine regenerative outcomes relevant to many diseases, including fibrosis. While many studies have shed light on stem-cell intrinsic mechanisms that govern their ability to switch identities, much less is known about microenvironmental factors that alert stem cells and modify their lineage decisions. Fibroblasts are structural cells that provide the necessary scaffolding for stem cells in their native niche, but fibroblasts also sense external changes to the tissue environment to drive the tissue response. In this review, we explore the role of fibroblasts as a critical orchestrator of lineage plasticity that blurs compartmental identities to initiate proper repair or disease.